1. Field of the Invention
The invention relates to a dental syringe for dentists, especially to a dental syringe of which the nozzle can be easily fitted and removed, and a nozzle-holding means with which the glove or even the fingertip of the dentist will not be liable to be pinched.
2. Description of Related Art
Dentists often use a drill to grind and clean the cavities in teeth, and use a dental syringe, containing either water or gas, to flush or blow away the bits produced by the drilling.
Shown in FIGS. 5 and 6 is a conventional dental syringe (2) for dentists, consisting of a head (21), a handle (22), a holding device (23), and a nozzle (24). The nozzle (24) includes a first end, and a second end with a circumferential under cut defined near thereto. The nozzle (24) has a major diameter and the under cut has a minor diameter. The head (21) has a male thread (211) thereunder used to engage with a female thread (221) defined in the top of the handle (22). In use, the first end of the nozzle (24) can be inserted in a patient's mouth to align with a cavity needed to be flushed. For reasons of hygiene, the nozzle (24) must be changed usually at least once for each patient. The second end of the nozzle (24) is affixed to the head (21) by means of the holding device (23) received in an opening (212) defined in the front of the head (21). The holding device (23) includes a pipe (231) having a male thread for engaging with a female thread defined in the opening (212), a small barrel (232) covering and being slidable along the pipe (231), and a spring (233) being pressed between a bottom of the barrel (232) and a bottom of the opening (212). In a non-retracted mode of the dental syringe, the barrel (232) is pushed away from the head (21) by the spring (233) and covers a plurality of balls disposed in the pipe (232) thus pressing them radiallyinward to a first position. The balls in the first position describe a diameter that is equal to the minor diameter but smaller than the major diameter of the nozzle (24) and thus the second end of the nozzle (24) cannot enter the head (21). When the nozzle (24) is to be inserted in the head (21), a dentist must pull the barrel (232) backward against the spring (233) whereafter the balls are free to move to a second position where they describe a diameter greater than the major diameter of the nozzle (24), such that the second end thereof can enter the head (21). Then the dentist releases the barrel (232) which is accordingly pushed back to its original position of the non-retracted mode, thereby urging the balls radially inward to be received in the under cut, whereby the nozzle (24) is securely retained in the head (21). Reversal of the above process enables the nozzle (24) to be removed from the head (21). From the above description, the conventional dental syringe for dentists has following shortcomings:
1. in both assembly and removal , dentists have to simultaneously grasp the nozzle (24), hold the handle (22), and push the barrel (232) which requires considerable dexterity. PA1 2. after releasing the barrel back, a glove or even a hand of the dentist is often pinched between the pipe (24) and the barrel (232).